#include <fcntl.h>
       #include <stdlib.h>
       #include <unistd.h>
       #include <stdio.h>
       #include <errno.h>
       #include <aio.h>
       #include <signal.h>

       #define BUF_SIZE 20     /* Size of buffers for read operations */

       #define errExit(msg) do { perror(msg); exit(EXIT_FAILURE); } while (0)

       #define errMsg(msg)  do { perror(msg); } while (0)

       struct ioRequest {      /* Application-defined structure for tracking
                                  I/O requests */
           int           reqNum;
           int           status;
           struct aiocb *aiocbp;
       };

       static volatile sig_atomic_t gotSIGQUIT = 0;
                               /* On delivery of SIGQUIT, we attempt to
                                  cancel all outstanding I/O requests */

       static void             /* Handler for SIGQUIT */
       quitHandler(int sig)
       {
           gotSIGQUIT = 1;
       }

       #define IO_SIGNAL SIGUSR1   /* Signal used to notify I/O completion */

       static void                 /* Handler for I/O completion signal */
       aioSigHandler(int sig, siginfo_t *si, void *ucontext)
       {
           if (si->si_code == SI_ASYNCIO) {
               write(STDOUT_FILENO, "I/O completion signal received\n", 31);

               /* The corresponding ioRequest structure would be available as
                      struct ioRequest *ioReq = si->si_value.sival_ptr;
                  and the file descriptor would then be available via
                      ioReq->aiocbp->aio_fildes */
           }
       }

       int
       main(int argc, char *argv[])
       {
           struct ioRequest *ioList;
           struct aiocb *aiocbList;
           struct sigaction sa;
           int s, j;
           int numReqs;        /* Total number of queued I/O requests */
           int openReqs;       /* Number of I/O requests still in progress */

           if (argc < 2) {
               fprintf(stderr, "Usage: %s <pathname> <pathname>...\n",
                       argv[0]);
               exit(EXIT_FAILURE);
           }

           numReqs = argc - 1;

           /* Allocate our arrays */

           ioList = calloc(numReqs, sizeof(struct ioRequest));
           if (ioList == NULL)
               errExit("calloc");

           aiocbList = calloc(numReqs, sizeof(struct aiocb));
           if (aiocbList == NULL)
               errExit("calloc");

           /* Establish handlers for SIGQUIT and the I/O completion signal */

           sa.sa_flags = SA_RESTART;
           sigemptyset(&sa.sa_mask);

           sa.sa_handler = quitHandler;
           if (sigaction(SIGQUIT, &sa, NULL) == -1)
               errExit("sigaction");

           sa.sa_flags = SA_RESTART | SA_SIGINFO;
           sa.sa_sigaction = aioSigHandler;
           if (sigaction(IO_SIGNAL, &sa, NULL) == -1)
               errExit("sigaction");

           /* Open each file specified on the command line, and queue
              a read request on the resulting file descriptor */

           for (j = 0; j < numReqs; j++) {
               ioList[j].reqNum = j;
               ioList[j].status = EINPROGRESS;
               ioList[j].aiocbp = &aiocbList[j];

               ioList[j].aiocbp->aio_fildes = open(argv[j + 1], O_RDONLY);
               if (ioList[j].aiocbp->aio_fildes == -1)
                   errExit("open");
               printf("opened %s on descriptor %d\n", argv[j + 1],
                       ioList[j].aiocbp->aio_fildes);

               ioList[j].aiocbp->aio_buf = malloc(BUF_SIZE);
               if (ioList[j].aiocbp->aio_buf == NULL)
                   errExit("malloc");

               ioList[j].aiocbp->aio_nbytes = BUF_SIZE;
               ioList[j].aiocbp->aio_reqprio = 0;
               ioList[j].aiocbp->aio_offset = 0;
               ioList[j].aiocbp->aio_sigevent.sigev_notify = SIGEV_SIGNAL;
               ioList[j].aiocbp->aio_sigevent.sigev_signo = IO_SIGNAL;
               ioList[j].aiocbp->aio_sigevent.sigev_value.sival_ptr =
                                       &ioList[j];

               s = aio_read(ioList[j].aiocbp);
               if (s == -1)
                   errExit("aio_read");
           }

           openReqs = numReqs;

           /* Loop, monitoring status of I/O requests */

           while (openReqs > 0) {
               sleep(3);       /* Delay between each monitoring step */

               if (gotSIGQUIT) {

                   /* On receipt of SIGQUIT, attempt to cancel each of the
                      outstanding I/O requests, and display status returned
                      from the cancellation requests */

                   printf("got SIGQUIT; canceling I/O requests: \n");

                   for (j = 0; j < numReqs; j++) {
                       if (ioList[j].status == EINPROGRESS) {
                           printf("    Request %d on descriptor %d:", j,
                                   ioList[j].aiocbp->aio_fildes);
                           s = aio_cancel(ioList[j].aiocbp->aio_fildes,
                                   ioList[j].aiocbp);
                           if (s == AIO_CANCELED)
                               printf("I/O canceled\n");
                           else if (s == AIO_NOTCANCELED)
                                   printf("I/O not canceled\n");
                           else if (s == AIO_ALLDONE)
                               printf("I/O all done\n");
                           else
                               errMsg("aio_cancel");
                       }
                   }

                   gotSIGQUIT = 0;
               }

               /* Check the status of each I/O request that is still
                  in progress */

               printf("aio_error():\n");
               for (j = 0; j < numReqs; j++) {
                   if (ioList[j].status == EINPROGRESS) {
                       printf("    for request %d (descriptor %d): ",
                               j, ioList[j].aiocbp->aio_fildes);
                       ioList[j].status = aio_error(ioList[j].aiocbp);

                       switch (ioList[j].status) {
                       case 0:
                           printf("I/O succeeded\n");
                           break;
                       case EINPROGRESS:
                           printf("In progress\n");
                           break;
                       case ECANCELED:
                           printf("Canceled\n");
                           break;
                       default:
                           errMsg("aio_error");
                           break;
                       }

                       if (ioList[j].status != EINPROGRESS)
                           openReqs--;
                   }
               }
           }

           printf("All I/O requests completed\n");

           /* Check status return of all I/O requests */

           printf("aio_return():\n");
           for (j = 0; j < numReqs; j++) {
               ssize_t s;

               s = aio_return(ioList[j].aiocbp);
               printf("    for request %d (descriptor %d): %zd\n",
                       j, ioList[j].aiocbp->aio_fildes, s);
           }

           exit(EXIT_SUCCESS);
       }

